1. Field of the Invention
The present invention relates to a method for implementing a microencapsulation of phosphor particles or transparent conducting particles using a phosphor material to improve a luminous efficiency of a cathodoluminescent and a method for forming a cathodoluminescent screen using the same for a field emission display, and more particularly to a method for forming a cathodoluminescent screen provided with uniform cathodoluminescent phosphor-coated particles for a field emission display by a method such as an electrodeposition, a screen printing, or a spray by using the phosphor-coated particles.
2. Description of the Related Art
Phosphor particles are used in a variety of applications such as a flat panel display and decoration, cathode ray tube, and fluorescent lighting fixture. Luminescence or light emission from phosphor-coated particles may be stimulated by applying of heat, light, high energy radiation, or electric fields.
It has been recognized that various improvements in the performance of phosphors can be obtained if the phosphor material is coated with a protective film or pigment. Numerous attempts have been made to coat the outer surfaces of individual particles with a protective coating material.
U.S. Pat. No. 4,508,760 discloses an encapsulation technique of phosphor particles by a vacuum deposition using a certain polymer.
U.S. Pat. No. 4,515,827 is achieved by disclosing phosphor particles coated by the color modifying material while the particles are rotated in a vacuum chamber.
U.S. Pat. No. 4,585,673 discloses the formation of a continuous protective coating on phosphor particles by gas-phase chemical vapor deposition while the phosphor particles are suspended within a fluidized bed.
U.S. Pat. No. 4,515,827 discloses encapsulated cathodoluminescent phosphor particles by a vapor phase hydrolysis reaction of oxide precursor material.
U.S. Pat. No. 5,156,885 discloses encapsulated phosphor particles by a low temperature vapor phase hydrolysis reactions and deposition process.
In the above coating techniques, the movement, rotation, or vibration of the particles was necessary for a uniform film growth because it was very hard to deposit uniform, conformal continuous, and stoichiometric thin film or particles.
Also, the cathodoluminescent films of the cathodoluminescent screen of a cathode-ray tube, such as a color cathode-ray tube or a monochromatic cathode-ray tube, are formed principally by a slurry process, and the cathodoluminescent films of the cathodoluminescent screen of some cathode-ray tubes are formed by a screens printing, a spray, or an electrodeposition process.
Generally, ZnO, ZnGa2O4: Mn, ZnGa2O4: Eu, YAG: Tb, Y2SiO5: Ce, Y2O3: Eu, Y2O2 S: Tb, Gd2 O2 S: Tb, SrS: Ce, SrTe: Ce, SrS-Sc2S3, ZnS: Ag, ZnS: Pr, SrGa2 S4, ZnCdS: Cu, Al are used for cathodoluminescent materials of the cathodoluminescent screen of a field emission display.
However, in the conventional cathodoluminescent particles to form a screen of a cathode ray tube, the surfaces of the particles are continuously polished and are exposed to a dilution liquid, so that the surface of the same may be changed, thus forming a dead layer and decreasing the characteristic of the cathodoluminescence of very surface region of the particles.
Therefore, in the industry, the technique for reducing the dead layer formed on the surface of the cathodoluminescent particle becomes an important technique.
The conventional phosphor particles used in the thick film type will be explained with reference to FIGS. 1A and 1B.
FIGS. 1A and 1B are cross-sectional views showing conventional phosphor particles and a cathodoluminescent screen using the same for a field emission display, respectively.
As shown in FIG. 1B, a transparent conductive layer 2 is formed on the transparent substrate 1. A cathodoluminescent films 3a composed of phosphor particles 3 of the FIG. 1 on the transparent conduction layer 2 is formed using phosphor-coated particles 3 of fine powder types having a diameter of less than 10 micron in average particle size by a screen printing, a spray, or an electrodeposition process.
FIG. 2 is a cross-sectional schematic drawing of a field emission display showing an electron emission tip, or field emission cathode, surrounded by the self-aligned gate structures.
Referring to FIG. 2, the electron emission tip 4 is integral with the single crystal semiconductor substrate 5, and serves as a cathode conductor. Gate 8 serves as a low potential anode or grid structure for its respective cathode 4. A dielectric insulating layer 7 is deposited on the conductive cathode layer 6. The insulator 7 also has an opening at the field emission site location.
A field emission display employing a cold cathode is depicted. The substrate 5 can be comprised of glass, for example, or any of a variety of other suitable materials, In the preferred embodiment, a single crystal silicon layer serves as a substrate 5 onto which a conductive material layer 6, such as doped polycrystalline silicon has been deposited. At a field emission site location, a conical micro-cathode 4 has been constructed on the top of the substrate 5. Surrounding the micro-cathode 4, is a low potential anode gate structure 8. When a voltage is applied between the cathode 4 and the gate 8, a stream of electrons 9 is emitted toward a phosphor-coated screen 1. Screen 1 is an anode and includes cathodoluminescent material 3 on its surface. The display faceplate cover with the included cathodoluminescent layer is distantly disposed with respect to the electron emission structure. Same of emitted electrons of will impinge upon the cathodoluminescent material, and at least some of the energy of the emitted electrons is converted to photon energy as visible light. The visible light is transmitted through the transparent conduction layer 2 and the transparent substrate 1 of the display to the viewer.
The purity and intensity of light is determined by composition, uniformity and surface state of the phosphor particles. Luminous efficiency of the cathodoluminescent films formed by the thick film type is particularly determined by uniformity of the particle size and surface state of the particle. Also, the photoemission from the thin surface layer of phosphor particles becomes more important in the field emission display operated by lower acceleration voltage of electron beam.
When phosphor particles of the FIG. 1 are formed by a conventional technique, a dead layer (non-luminescent on the particle surface is formed by continuously polishing or by exposing in the dilution with destructive state. Therefore, such conventional invention of the thick film type has been reduced luminous efficiency.
Also, if acceleration voltage of the electron beam is low, a photoemission region is thinly formed, the thinnest surface of the cathodoluminescent layer is emitted. Therefore, the surface state of the phosphor particles have influence on the luminous efficiency.
Disadvantages associated with these known methods are eliminated by the method of the present invention by which a thin phosphor film having a desired substantially uniform thickness is formed by an atomic layer deposition on the outer surface of the phosphor particles or the transparent conducting particles.
Accordingly, an object of the present invention is to provide a method for coating phosphor layer on the phosphor particles and the transparent conducting particles by an atomic layer deposition to improve the luminous efficiency of the cathodoluminescent films for a field emission display and which does this while avoiding the disadvantages of the prior art.
It is another object of the present invention to provide a method for forming a cathodoluminescent screen by forming cathodoluminescent films on the inner surface of screen panel for a field emission display by a method such as a screen printing, a spray and an electrodeposition process.
To achieve the above objects, there is provided field emission display cathodoluminescent particles for improving a luminescent emission efficiency according to a first embodiment of the present invention, wherein the improved cathodoluminescent particles are formed by coating a uniform cathodoluminescent material on the surfaces of cathodoluminescent particles by an atomic layer deposition.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to a second embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, on which a uniform cathodoluminescent material is coated by an atomic layer deposition, on the surface of a field emission display unit by an electrophoretic deposition method.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to a third embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, on which a uniform phosphor material is coated by an atomic layer deposition, on the surface of a field emission display unit by a screen printing method.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to a fourth embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, on which a uniform phosphor material is coated by an atomic layer deposition, on the surface of field emission display screen unit by a spray method.
To achieve the above objects, there is provided field emission display cathodoluminescent particles for improving a cathodoluminescent efficiently according to a fifth embodiment of the present invention, wherein the improved field emission display cathodoluminescent particles are formed by coating a uniform cathodoluminescent material on the surfaces of transparent conducting particles by an atomic layer deposition.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to a sixth embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, which are formed by coating uniform cathodoluminescent material on the surface of transparent conducting particles by an atomic layer deposition, on a screen of the field emission display unit by an electrophoretic deposition method.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to a seventh embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, which are formed by coating an uniform cathodoluminescent material on the surface of transparent conducting particles by an atomic layer deposition, on the screen of a field emission display unit by a screen printing method.
To achieve the above objects, there is provided a field emission display cathodoluminescent layer forming method including a transparent substrate and a transparent electrode layer formed on the transparent substrate according to an eighth embodiment of the present invention, wherein the improved method is directed to forming cathodoluminescent particles, which are formed by coating uniform cathodoluminescent material on the surface of transparent conducting particles by an atomic layer deposition, on the sereen of a field emission display unit by a spray method.
Atomic layer deposition is a chemical thin film deposition method based on saturation surface reactions. The unique feature of atomic layer deposition is that reactant vaporsxe2x80x94elements or compoundsxe2x80x94are pulsed onto the substrate alternately, one at a time. Between the reactant pulses the reactor is either purged with an inert gas or evacuated. With a proper adjustment of the experiment conditions, i.e. substrate temperature, reactant doses and lengths of pulse a chemisorbed monolayer of the first reactant is retained on the substrate after the purge sequence. This chemisorbed monolayer reacts subsequently with the other precursor dosed onto the substrate resulting in a solid film and, if compounds are exploited as precursors, gaseous byproducts. By repeating this deposition cycle the film is grown layer-by-layer. However, due to steric hindrances of bulky precursor molecules and surface reconstructions, the surface density of chemisorbed species remains often too low for a formation of a complete crystal layer of the film during one cycle. Nevertheless, the film thickness is still only a function of the number of deposition cycles repeated. As a result, the growth is said to be self-controlled or self-limited.
Also, in accordance with a preferred embodiment of the present invention, there is provided a method of forming a cathodoluminescent screen for a field emission display by depositing particles of a cathodoluminescent material or cathodoluminescent materials on the inner surface of a screen panel by an elctrodeposition process.
A method of forming a cathodoluminescent film by an electrodeposition process in accordance with the present invention forms on the inner surface of a screen panel for a field emission display comprising: immersing the screen panel in an electrodeposition solution in which particles of a cathodoluminescent material is dispersed, applying a negative voltage on the transparent conduction layer and a positive voltage a counter electrode immersed opposite to each other in an electrodeposition solution prepared by dispersing particles of a cathodoluminescent material in an electrolyte for positively or negatively charging the particles of the cathodoluminescent material, a negative voltage and a positive voltage are applied respectively to the transparent electrode of the screen panel and the counter electrode when the cathodoluminescent material is positively charged to deposit the cathodoluminescent material over the surface of the electrode, washing and drying the screen panel after the cathodoluminescent film has been formed.
Also, a method of forming a cathodoluminescent film of the cathodoluminescent screen by a screen printing or a spray deposition process in accordance with the present invention for a field emission display comprises: mixing a paste or a solvent and a phosphor-coated particles, forming on the inner surface of a screen panel by the screen printing or the spray method.